1. Field of the Invention
The present invention relates to a method and application thereof for determining abnormities in a dataset, and more particularly to a method and application thereof for determining a defect from a charged particle microscopic image of a sample.
2. Description of the Prior Art
During charged particle beam inspection of a sample, a charged particle microscopic image is formed from the secondary charged particles released from the sample while it is being bombarded by a primary charged particle beam. By analyzing the charged particle microscopic images, desired information of the physical and electrical characteristics of the inspected sample can be obtained. For example, the charged particle beam imaging technique is applied to the inspection of a semiconductor device, and by analyzing the obtained image of the semiconductor device the presence of defects in the concerned device can be determined.
FIG. 1 schematically illustrates a method for determining a defect during charged particle beam inspection of a sample according to the prior art. First, a charged particle microscopic image 1 is obtained by processing an image data stream extracted from secondary charged particle signals emitted by a sample being inspected. Next, as shown a key-shaped pattern 11a and 12a are identified from image 1. The identification of pattern 11a and 12a is based on certain predefined rules. For example, a rule which defines the shape of data that should contain information of pattern 11a and 12a is selected to be applied for directly identifying such pattern-representing data from the image data stream. Then, the identified patterns 11a, 12a are reproduced in the image and compared with a reference database graphic to determine the presence of a defect (for example label 122 shown in FIG. 1) in patterns 11a and 12a. 
The reference database graphic represents a pattern layout corresponding to that in image 1 and can be, for example, a Graphic Data System (GDS) or Open Artwork System Interchange Standard (OASIS), etc. data file of an area on the sample which is represented by image 1. In this embodiment, the reference database graphic contains reference patterns 11b and 12b respectively corresponding to patterns 11a and 12a. As illustrated in FIG. 1, edges 111a and 121a of patterns 11a and 12a are aligned then compared with the corresponding edges 111b and 121b in the reference patterns 11b and 12b for estimating an excursion of the fabricated patterns from the original design. For example, a distance between edges 121a and 121b can be compared for individual point on the edge, or can be compared as a whole through statistical approaches, so as to determine the presence of defect 122. It is noted that in order to distinctly illustrate the idea, an exaggerated shift is shown between patterns 11a, 12a and the corresponding reference pattern 11b and 12b in FIG. 1.
In foregoing prior art, patterns 11a, 12a are identified directly from (the data stream of) image 1 based on certain predefined rules. However, there are difficulties implementing such methodology. For example, some of the rules for identifying the pattern-representing data are more like a guidance of what data sectors to be paid attention to, rather than an exact indicator of the data sectors to be selected. As a result, the identified pattern-representing data could in fact be representing a “false” pattern rather than the real interested one.
According to the foregoing descriptions, the conventional defect determination method for the charged particle beam inspection is not generally reliable. Therefore, a method to more accurately determine a defect from a charged particle microscopic image is desirable.